1. Field of the Invention
The present invention relates to a curable organopolysiloxane composition and particularly to a curable organopolysiloxane composition suitable for use in release purposes, particularly release papers. 2. Description of Prior Art
Heretofore, silicone films have been formed on substrates to give releasability to their surfaces for the purpose of preventing adhesive materials from strongly adhering to the surfaces and being peeled therefrom with difficulty.
For the formation of such silicone films, there have been generally used silicone compositions comprising an organopolysiloxane having an aliphatic unsaturated hydrocarbon group and an organohydrogenpolysiloxane having a silicon-bonded hydrogen atom, which may undergo addition reaction in the presence of a platinum catalyst to give a cured product As the organohydrogenpolysiloxane in such silicone compositions, has been used a methylhydrogenpolysiloxane having the following structure unit containing the hydrogen atom bonded to the silicon atom: ##STR2## Such a methylhydrogenpolysiloxane is represented, for example, by the formula: ##STR3## wherein b and c are each an integer.
However, where a silicone film is formed using the silicone composition as described above, the force necessary to peel a sticking adhesive applied to the silicone film from the silicone film (which force is hereinafter referred to as "peel force") has a tendency to gradually decrease with the passage of time from the formation of the silicone film to the application of the sticking adhesive on the silicone film. Also, the peel force has a tendency to gradually increase with the passage of time from the application of a sticking adhesive on the cured silicone film to the peeling of the adhesive from the silicone film. Thus, the release properties of the silicone films have a tendency to change with the passage of time. This tendency is greater where acrylic adhesives are used or where the amount of the silicone applied is small.
Moreover, the change of the release properties of the silicone films as mentioned above is remarkable when the silicone is insufficiently cured because of excessively low curing temperature or excessively short curing time. Therefore, controlling of the change of the release properties with time has been attempted by raising curing temperature or extending curing time. However, heating at high temperatures or for a long period of time is not only unfavorable in view of the loss of energy and the lowering of production efficiency, but also cannot necessarily give satisfactory release properties stable for a long time.